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Post by Grey on Jan 20, 2014 22:26:29 GMT 5
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Post by theropod on Jan 21, 2014 2:23:14 GMT 5
The hand-held tooth is definitely more gracile, but thatÂ’s not necessarily the widest. HubbellÂ’s tooth is very broad, resembling an upper lateral (or certain UA3Â’s, see the variation in the tooth set) while that one looks like an anterior one, and perhaps from the lower jaw.
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Post by Grey on Jan 21, 2014 2:55:23 GMT 5
Gordon had said his tooth is an upper anterior even though I had wondered too about its actual position. I'm not sure of the position of Klaus tooth but I'm not sure he would have showed a lower anterior for the pic. There is also that tooth that I don't know if it is isolated or not.  |
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Post by theropod on Jan 21, 2014 17:38:20 GMT 5
Hmm, Hubbell´s tooth is proportioned similar to an upper lateral. Are there any diagnostic features that show it is an UA?
The second picture definitely resembles a lower-jaw tooth the most (why should he not have showed one?), I dont think we´ve got any reason to presume it is the same position as Hubbells tooth considering how different they are in shape.
The last tooth you posted looks really big, any known measurements?
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Post by Grey on Jan 21, 2014 23:08:42 GMT 5
There's no diagnostic feature that I know of that tooth in scientific records neither in fossils websites. But Gordon Hubbell states it as an upper anterior : www.youtube.com/watch?v=TUyWbW3yKFIGordon Hubbell is a world reference in sharks dentitions studies since decades, treated with great respect by sharks experts, so I think he might know what he's stating. I think that Klaus wouldn't show a lower anterior as they are typically a bit less spectacular (built for seizing, not sawing) than upper anteriors. That tooth is more gracile than Hubbell's but it is not necessary from the exact same position. And simply, perhaps the Hubbell's shark was even older, bigger, than Klaus specimen. My guess is that both are upper front teeth but not from the same position. I don't know the size of that tooth in my last pic, Klaus indications were alsays a bit confusing but I wouldn't be surprised if it's a 7 incher. Problem is that it's difficult to judge by the hands of the guy. For example, Hubbell's tooth is absolutely huge but it appears that Mark Renz who handle it in the video has massive hands. Such a large tooth would look different in my hands (somewhat smallish for my size). |
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Post by theropod on Jan 21, 2014 23:49:17 GMT 5
Scientists arenÂ’t always that focused on showing the most spectacular stuff. Also, there wasnÂ’t even an official release so far. That they are not from the same position was exactly my point, that doesnÂ’t have to mean the two specimens couldnÂ’t have been similar-sized. If HubbellÂ’s tooth is an anterior, itÂ’s most similar to the freakingly wide UA3 on the right hand side here:  Thus very likely not the same position as the considerably more gracile specimen, whether the latter is mandibular tooth or palatoquadratal. ItÂ’s not as much a size difference as a shape difference. |
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Post by Grey on Jan 22, 2014 0:04:29 GMT 5
I think too it's an UA3, not because of its size, it's simply a massive tooth from a massive shark, but because of it's proportions (shorter side than the other). Remarkably, this suggests there was likely a wider tooth in the dentition.
Klaus just shows its most remarkable findings in his pics, it's seems clear to me by its size that this tooth is an upper. Or then if it's a lower, the upper would be absolutely huge.
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Post by theropod on Jan 22, 2014 1:26:31 GMT 5
The slant proportions arenÂ’t significantly different among the anteriors and anterior laterals. What sets them apart is the width/height ratio, middle laterals and in some cases UA3s being fairly wide and squat (just like HubbellÂ’s tooth) while UA1 and UA2 tend to be more slender. But of course thereÂ’s a lot of variation, for example the right UA3 is 9% wider than the left in HubbellÂ’s set, even though they are the same height.
Lower teeth can also be quite long, what sets them apart is mostly their more narrow shape, which fits the shape of that specimen (based on the associated dentitions IÂ’d guess LA1).
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Post by creature386 on Jan 22, 2014 2:50:21 GMT 5
Is there that much of a difference between upper and lower teeth? I have seen distinction between anterior and posterior teeth in papers (like Pimiento et al. 2010), but they didn't bother explaining the differences between upper and lower teeth.
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Post by theropod on Jan 22, 2014 19:33:08 GMT 5
Lower teeth (not just in C.megalodon) tend to be more pointed and narrower, built more-so for easy puncturing and securing of the prey item than for slashing through it (broad teeth are usually associated with slicing in sharks, while narrower teeth are associated with gripping). You can see it in the associated dentition, the lower ones are noticeably smaller and more gracile.
Of course teeth have varying degrees of robusticity, and are quite variable even for the same position. This is just a general trend, it doesnÂ’t mean this must necessarily be a mandibular tooth, but it seems to resemble them more, and is thus reasonable to assume.
I presume these two specimens may be similar-sized because both the total lenght figures I listed (except GottfriedÂ’s) and the tooth lenght (that is slant-lenght) are roughly comparable to the reported measurements from the larger Peruvian specimen.
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Post by Grey on Feb 12, 2014 5:59:20 GMT 5
Not sure what means the vertical lines above and below the squares representing Megalodon's body mass in Balk's graph here. If it actually represents the actual range of body mass of Megalodon in each period, this would mean that at 12 MYA, log Megalodon mass peaks at 4.86, which translantes exactly in at 73.82 tonnes, let's say roughly 70 tonnes. Note that it is not sure if the vertical line (range ?) ends at this or no given the graph stops there. Maybe coherentsheaf can say more about the significance of these lines (and what means also the two joined squares in each period), the meaning being maybe totally different. Again remember that all the data was not collected yet at the time this graph was made.  |
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Post by theropod on Feb 12, 2014 14:35:13 GMT 5
That’s a boxplot?. The lines mark the complete range of all the data. The box is the distance between the 2nd and 3rd quartiles. |
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Post by Grey on Feb 12, 2014 16:25:57 GMT 5
Does that mean the peak Megalodon in that graph is at >70 tonnes and the smallest just under 100 kg (embryonic ?) ?
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Post by creature386 on Feb 12, 2014 17:14:09 GMT 5
Probably.
As for the significance of this, normally in a boxplot, you list all the numbers and the one in the middle is the median then, but for calculating the average mass of an animal, you count everything together and then divide. Do you think this method is good for determining the average size?
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Post by coherentsheaf on Feb 12, 2014 17:27:01 GMT 5
theropod it is a bit more complicated. Normally the lines go to up to 1.5 times the interquartile distance and not all the way. Things outside this disatace are shown as dots. But fr the purpose of this thread you are close eough. So the largest Megalodon in their sample measured 70+tonnes? I would love to see how they did the estimate.
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